The Story
About half a minute in, two clear whistled notes arrive, the second lower than the first. That is the fee-bee song of the black-capped chickadee, and it does a very different job from the chick-a-dee call.
The picture carries the field marks: black cap, black bib, white cheeks, a buff wash down the sides. The bird sits on a bare twig with its bill open against a soft gray blur. What the picture cannot settle is the sex. Males use the fee-bee, but male and female look identical.
The whistle is a property claim. Males use it to set up territories and attract mates, mostly in late winter and spring. Pairs typically form in fall and stay in the winter flock, then the flock breaks up in late winter and each pair defends 1.5 to 5.3 hectares. That is a lot of real estate to hold with two notes and a body of 0.3 to 0.5 ounces.
The species has far more to say than that. Adults make as many as 16 different calls. A sharp zeet goes up at the sight of a predator, and groups mob predators to scare them away. In the chick-a-dee call, more dee notes generally mean a greater threat, and experiments with 15 live predator species found that mobbing calls varied with predator size.
Chickadees are not the only ones paying attention. Other songbirds, especially passing migrants, tend to tag along to listen for chickadee feeding and alarm calls. Around the 56-second mark a different bird starts up in the background here. It goes unnamed, and nothing shows it is listening in.
One catch for anyone matching this whistle outdoors. The Carolina chickadee is almost identical and best told apart by range, and in the overlap zone each species can learn the wrong song. There, two clean notes can name the wrong bird.
